The properties of calcium phosphate salts of biological interest are being studied with a variety of ultrastructural and physical-chemical techniques such as electron microscopy, x-ray diffraction, B-E-T surface area methods, chromatograplhic and standard analytical chemistry procedures. Topics under current investigation include (1) the preparation and characterization of synthetic analogues to intracellular mineral deposits such as occur in mitochondria and in subcellular storage organelles, (2) the formation and properties of precipitates induced in phosphate solutions by the ionophoric translocation of Ca ions across lipophilic solvent barriers, and (3) the modulation by enamel proteins of crystal growth processes in supersaturated solutions seeded with apatite.